Bone grafting is a surgical procedure that replaces missing bone. Bone grafts may be autologous, which are grafts harvested from a patient's own body, allograft, which are cadaveric grafts obtained from a bone bank), or synthetic grafts. Dental bone grafts may be performed to reverse bone loss or destruction caused by, for example, periodontal disease or trauma. Some bone grafts are performed to rebuild bone structure to support dental implants. Membranes may be used to stabilize the bone graft as it heals. Use of membranes also helps prevent gum tissue from displacing the bone graft before it matures. Sinus lifts are bone grafting procedures for patients with bone loss in the upper jaw (maxilla). The bone graft material is placed in the space between the sinus membrane and sinus bony floor to help the body grow bone and form a thicker sinus floor. Once the bone graft site has healed, the jaw bone below the sinus may be used for dental implants. These bone graft procedures are highly-complex procedures requiring a large amount of training on behalf of an oral surgeon before he can proficiently operate on a human patient.